Exoskeletons: A Primer

With applications ranging from the military to medical rehabilitation to life-changing assistance for the handicapped, several companies are betting their new-generation exoskeletons will become robotics’ next big thing

An exoskeleton, also called a wearable robot, differs from other types of robotic devices in that it provides a shell or framework (skeleton) on the outside of a person’s body and essentially acts as an extension of that individual’s body. Probably the most familiar exoskeleton robots come from popular culture—comic books and movies such as the man/suit combination in the film Iron Man and the fighting robots in Avatar.

Exoskeleton robots may be classified as delivering two different kinds of service to users: orthosis and augmentation.

Orthosis: Providing support and/or motion to a limb or other body part or parts that have diminished capacity due to disease or injury. Orthotic exoskeletons may be used in physical therapy in a clinical environment, or in the daily life of patients. Some newer models even make it possible for a paralyzed person to walk instead of using a wheelchair. Note that a prosthesis—an artificial limb—can be a robotic device, but because it does not surround or work in parallel with a living body part, it is not considered an exoskeleton and not covered here. Robotic prostheses do have many of the same mechanical, sensing, control, and power management issues as exoskeleton robots.

Augmentation: Increasing the ability of an able-bodied human to move faster, lift heavier loads, carry more, or exhibit greater endurance. This category of exoskeletons can fulfill needs in military, industrial, and healthcare applications. Because they can carry heavy loads and perhaps move faster over rough ground, augmentative exoskeletons need to be stronger and more rugged than rehabilitative exoskeletons. s

Market Prospects

Some exoskeleton robots have already reached the market and are able to function in various environments, if only as a proof of concept or beta-stage launch. More are in the introductory or development stages. The prospective markets for these devices are quite large and promise significant growth in the coming years, as product becomes available and affordable. Last January, ABI Research predicted the market for would reach $877 million by 2020.

Lower-body, untethered orthotic exoskeleton robots for daily use by the disabled could enable some people who are paralyzed to walk again. Currently, this group numbers roughly 6 million in the United States alone, according to a study initiated by the Christopher & Dana Reeve Foundation. People with less severe disabilities also could make use of orthotic exoskeleton robotics for specific functions, such as the foot-ankle active orthosis discussed below. The need already exists for these specialized robots, and only awaits cost-effective products to satisfy it. Insurance reimbursement will be an important factor influencing demand for these daily-use products.

Various exoskeleton models used in physical therapy have already been deployed in rehabilitation centers, for both lower-limb and upper-limb therapy. Only a few locations currently possess such equipment, however, so this market offers significant opportunities. In addition, with an aging population and ongoing improvements in treatment and rehabilitation for stroke and other conditions, the need for rehabilitative exoskeletons can only grow. Information is not readily available projecting specific disabilities that could be aided by the technology among patient populations. But one indicator is the demand for physical therapists, which is expected to increase by 30 percent from 2008 to 2018, according to the U.S. Bureau of Labor Statistics. Thus, demand for supporting technology will likely grow in tandem over the same period.

Augmentation exoskeleton robots for the military, once they are fully developed, could conceivably be deployed by the thousands to aid troops on the ground. Industrial versions of exoskeleton robots descended from the military versions could find wide application for lifting and other common tasks in construction and on the factory floor, once robot production volume is sufficient to bring down prices. Since such devices could reduce back injuries and other mishaps, the cost of workers’ compensation insurance could be reduced, making exoskeletons especially attractive to industries where such injuries are common.

Exoskeletons Tasked with Helping the Injured and Disabled

Orthotic devices based on the exoskeleton model run the gamut from those designed to help a paralyzed person stand up and walk, to those intended to aid a single joint.

An exoskeleton robot for orthotic applications in physical therapy facilities, the Lokomat Pro from Hocoma Inc. USA, Rockland, Mass., supports the patient’s weight and, through powered segments fitted to the legs, automates the patient’s walking on a treadmill. The robotic exoskeleton attached to the patient’s legs is programmed to keep movements within the range of a normal walking gait. This type of therapy can replace walking practice sessions, where one physical therapist steadies the patient on a treadmill and two other therapists move the feet and legs through the motions of walking. The robot would yield significant savings in labor costs, and studies show positive outcomes from a robotic system are equal to or better than those achieved by the manual method.

eLegs from Berkeley Bionics, Berkeley, Calif., is a lower-body exoskeleton robot designed to help paraplegics stand and walk on their own. The device is scheduled for release in 2012 at rehabilitation facilities. Eventually, eLegs, or a follow-on version, should be available for daily wear. The technology is based on the BLEEX (Berkeley Lower Extremity Exoskeleton) developed at University of California, Berkeley.

Argo Medical Technologies, Yokneam Ilit, Israel, offers the ReWalk-I walking exoskeleton robot for institutional rehab use. It is currently available to medical facilities in the United States and Europe. The ReWalk-P, a version for personal daily wear, is expected to be available by the end of 2011.

Rex is another lower-body walking robotic exoskeleton for daily use by paralyzed people who otherwise use a wheelchair. It is currently available from Rex Bionics, Rosedale, New Zealand.

Honda Motor Company Ltd., Tokyo, has developed two experimental exoskeleton walking-assistance devices. One attaches at the user’s thighs and moves them to help maintain a strong walking stride. The other helps support the user’s weight, making it easier to climb stairs as well as to walk.

On a smaller scale, orthotic exoskeletons are being developed to aid particular localized needs, such as the active foot-ankle orthosis developed at Massachusetts Institute of Technology, Cambridge, Mass.

Augmenting Strength, Speed, Endurance

The current generation of augmentation exoskeleton robots includes two versions intended for military use. Lockheed Martin Corp., Bethesda, Md., developer of the HULC (Human Universal Load Carrier) announced in October 2010 the start of testing on an improved and ruggedized version of the exoskeleton robot. It is a lower-body unit designed to enable troops to carry loads of up to 200 pounds over rough terrain, transferring the load to the ground to reduce fatigue and prevent injury. HULC uses technology licensed from Berkeley Bionics, and is based on the BLEEX. Earlier this year, Lockheed Martin announced selection of Protonex Technology Corp. to develop a fuel-cell power supply to operate the HULC system to enable independent operation for 72 hours.

In the fall of 2010, Raytheon Co., Waltham, Mass., demonstrated the XOS 2, its second-generation full-body exoskeleton robot intended for the military market. A company executive says the unit will be available for tethered work in-theater in about five years, and for untethered operation roughly three to five years after that. A lower-body version allows for carrying heavy loads in the field. The full-body version will find applications in logistics, helping with material handling, including repetitive lifting of heavy items and containers.

Besides their uses in the military, versions of augmentation exoskeletons will undoubtedly find application in manufacturing and material handling to aid in heavy lifting, and in healthcare to help workers lift patients. Both could significantly reduce back injuries.

At the U.S. Consumer Electronics Show in January, Cyberdyne, Ibaraki, Japan, demonstrated Robot Suit HAL-5, a general-purpose augmentation exoskeleton robot, offering lower or upper/lower limb enhancement. HAL is currently available for monthly rental in Japan. According to company literature, applications may include rehabilitation, heavy labor in factories, disaster rescue, and entertainment.

Human + Machine

Exoskeleton robots have a unique relationship with their users. Essentially, the exoskeleton becomes an extension of the user. In a way, the user becomes part of the device, too, as the user may provide some of the intelligence that guides the robot. The task of the exoskeleton robot is twofold. First, determine or sense what the user wants to do. Then, do it.

At the U.S. Consumer Electronics Show in January, Cyberdyne, Ibaraki, Japan, demonstrated Robot Suit HAL-5, a general-purpose augmentation exoskeleton robot, offering lower or upper/lower limb enhancement. HAL is currently available for monthly rental in Japan. According to company literature, applications may include rehabilitation, heavy labor in factories, disaster rescue, and entertainment.

Human + Machine

Exoskeleton robots have a unique relationship with their users. Essentially, the exoskeleton becomes an extension of the user. In a way, the user becomes part of the device, too, as the user may provide some of the intelligence that guides the robot. The task of the exoskeleton robot is twofold. First, determine or sense what the user wants to do. Then, do it.

The various walking exoskeleton models use a variety of methods to detect where the user wants to go. BLEEX units, for instance, use many measurements from the exoskeleton to determine the user’s preferred direction with encoders, linear accelerometers, and force sensors measuring angle, angular velocity, and angular acceleration in the joints, and force distribution between the feet and the ground. The HAL-5 employs electrodes attached to the user’s thighs to detect intended movement, which will not work with some people with spinal cord injuries. eLegs uses instrumented crutches to help communicate the user’s desired direction. ReWalk users wear a small keypad on their wrists and touch the appropriate key for the desired motion—walking or climbing stairs, for example. The Rex robot has a joystick attached to the robot frame at the user’s waist.

One of the challenging aspects of untethered (self-sufficient) robots, which have to carry their power source with them, is providing sufficient energy storage capacity for fairly long operation before they’re required to stop to recharge or refuel. The Rex exoskeleton gives two hours of constant movement, which may be sufficient to make it through a day, since most of the time the user would be stationary. HAL-5 offers 160 minutes of operating time.

Most often, rechargeable batteries are used as a power source. An early version of one of the military models used a small internal combustion engine for power. The remedy is probably not ever going to be larger and larger batteries. Fuel cells may offer a solution. Increased energy storage capacity and/or reduced energy demand will likely be pursued as desirable options.

As an example of energy usage, one BLEEX exoskeleton robot that is hydraulically actuated required 1,143 watts when walking on a flat surface, plus 200 watts for its electronics and control systems. By contrast, the walking energy expenditure for a 75-kg (165-pound) person walking on level ground is a mere 165 watts.

Opportunities

Manufacturers of these robot systems would welcome improvements that can reduce the power draw, whether by decreasing the weight of the robot or increasing the efficiency of components.

Various exoskeleton robots have been driven with electric motors, hydraulics, pneumatics, and cable drives, or some combination of these mechanisms. Actuators need to not just do the job of providing torque to the joints, they must possess a small or sufficiently narrow form factor so as not to interfere with the user’s body. For both daily wear civilian units and military exoskeleton robots, noisy actuators are a problem. Excess noise on a military operation could alert the enemy to troops’ presence, and a disabled person walking with the aid of an exoskeleton robot doesn’t want to be made conspicuous due to a loudly running motor.

Improved or alternative technology actuators could also reduce energy usage and weight. Different exoskeleton robots have used electric, pneumatic, hydraulic, or cable actuators, or combinations. Artificial muscles may make ideal actuators when they are sufficiently developed.

Looking Ahead

In the future, exoskeleton robots will be lightweight, energy efficient, cost effective, and far quieter.

For industrial applications and the military, they will no doubt be adjustable to fit most workers or troops. Exoskeleton systems that people use at home every day to help them walk and perform activities of daily living will likely be custom fitted, using body scans that will permit them to perhaps be custom formed with state-of-the-art additive fabrication technology.

Eventually, electrodes implanted in the wearer’s brain may enable a direct connection between a user with a spinal cord injury and a daily-wear exoskeleton.

During the last few years several part- or full-body exoskeleton robots have been developed in different areas of the world. Some are at or near the point of becoming viable products. Their potential for use in the military, in industry, in healthcare, and as a life-enhancing technology for the disabled bodes well for their success.